Friday, February 2, 2018

Homodecoupling

Homodecoupling is a technique for selectively removing coupling in 1D NMR spectra. Often 1D 1H spectra show complex splitting patterns that are difficult to interpret. Selectively eliminating one coupling may allow a multiplet to be interpreted or enable measurement of couplings that could not otherwise be quantified. Recently, we used homodecoupling to assign the stereochemistry of a pair of enantiomers.

Wednesday, January 10, 2018

Gradients for measuring diffusion

Translational diffusion, also known as Brownian motion, is the random motion of particles among the other components of a solution. The rate of diffusion is related to the size of the molecule so measuring this rate can provide an estimate of molecular weight and information on aggregation, or binding, at close to physiological conditions. NMR experiments have been devised to measure translational diffusion using a pair of gradient pulses separated by a delay. These Diffusion Ordered SpectroscopY, or DOSY1, experiments, are typically shown as 2D spectra with a horizontal 1H dimension and a vertical diffusion rate dimension.

Thursday, December 7, 2017

Gradients for coherence selection

In addition to artifact suppression and removing solvent peaks, gradient pulses can be used for coherence selection. Traditionally, this was done by phase cycling but using gradients for coherence selection allows cleaner spectra to be obtained more quickly. In this post the use of gradients to select coherences in heteronuclear experiments is discussed.

Tuesday, November 14, 2017

Gradients for solvent suppression

The previous post described how a combination of gradients and pulses can be used to help reduce artifacts in NMR spectra. Adding a selective pulse to that sequence enables solvent signals to be excluded. This technique, sometimes known as excitation sculpting, is described below.

Tuesday, September 5, 2017

Gradients for removing artifacts

The previous post gave an introduction to gradient pulses, describing what they are. In this post, and the next few, I will describe a few applications of gradients. This post will describe how they can be used to reduce artifacts from imperfect pulses, allowing phase cycles to be reduced and experiments to be run more quickly.

Monday, August 7, 2017

Gradients

Gradients have become an essential part of modern NMR spectroscopy. Nearly all probes now have pulsed field gradient capabilities and the vast majority of pulse sequences use gradient pulses. In this post, and those following, I will try and explain what gradients are and how they can be useful.

Sunday, July 2, 2017

Sensitivity vs receiver gain

Recently I have noticed many users recording spectra with low values for the receiver gain. The receiver gain is a scaling factor for the FID signal that ensures spectra are not distorted if the signal is too large, or resolution is lost if the signal is too small. Typically the receiver gain is set automatically by the command "rga", but users should pay attention to the value obtained as it is a good indicator of how successful the experiment will be. To demonstrate this I measured sensitivity at different receiver gain values.